Real Estate Transactions - Development Activities (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) property	Jun. 30, 2019 USD ($)
Real Estate [Line Items]
Increase to development commitments | $		$ 82
Development commitments | $	$ 382	$ 382
Medical office
Real Estate [Line Items]
Number of properties to be developed (in properties) | property	3
On-campus
Real Estate [Line Items]
Number of properties to be developed (in properties) | property	2